The degrees of integration of integrated circuits have been increasing year by year. In producing semiconductor substrates such as VLSIs, it becomes necessary to form ultrafine patterns with a line width of a half micron or less. To satisfy this requirement, wavelength employed in alligners in photolithography has been more and more shortened and attempts are also made today to employ even far ultraviolet light and eximer laser beams (XeCl, KrF, ArF, etc.). Moreover, attempts have been also made to pattern at a further elevated degree of fineness by using electron beams or X-rays.
In particular, it has been required to develop negative resists for forming highly sensitive rectangular patterns with high resolution by using electron beams or X-rays which are considered as usable in the patterning techniques in the next generation or the subsequent generation.
In the electron beam lithography, a resist material is exposed to the energy emitted from an accelerated electron beam in the course of collision with atoms constituting the resist material and scattering. By using highly accelerated electron beams, the linearity is elevated and the effects of electron scattering is lessened, which makes it possible to form rectangular patterns with high resolution. On the other hand, the permeability of electron beams is elevated in such a case and thus the sensitivity is lowered. Thus, the sensitivity and resolution/resist pattern are compensated each other in the electron lithography. Therefore, it has been a problem how to manage both of these factors.
To cope with this situation, it has been a practice to use resists of the chemical amplification type mainly with the use of acid catalyst reactions to thereby elevate sensitivity. For negative resists, use has been effectively made of chemical amplification compositions containing alkali-soluble resins, acid-generating agents and acid crosslinking agents as the main components.
Concerning negative resists of the chemical amplification type, there have been proposed various alkali-soluble resins. For example, partly alkyl-etherified polyvinylphenols are disclosed by JP-A-8-152717; vinylphenol/styrene copolymers are disclosed by JP-A-6-67431 and JP-A-10-10733; novolak resins are disclosed by Japanese Patent NO.2,505,033; and monodisperse polyvinylphenols are disclosed in JP-A-7-311463 and JP-A-8-292559 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”). However, none of these alkali-soluble resins can establish both of sufficient sensitivity and resolution/resist pattern under the irradiation with electron beams or X-rays.
Concerning negative resists of the chemical amplification type, there have been proposed various acid-generating agents too. For example, organic halogen compounds are disclosed by JP-B-8-3635; iodonium salts and sulfonium salts are disclosed by JP-A-2-150848 and JP-A-6-199770; acid-generating agents containing Cl and Br are disclosed by JP-A-2-52348, JP-A-4-367864 and JP-A-4-367865; diazodisulfone and diazosulfone compounds are disclosed by JP-A-4-210960 and JP-A-4-217249; triazine compounds are disclosed by JP-A-4-226454; and sulfonate compounds are disclosed by JP-A-3-87746, JP-A-4-291259, JP-A-6-236024 and U.S. Pat. No. 5,344,742 (the term “JP-B” as used herein means an “examined Japanese patent publication”). However, none of these acid-generating agents can overcome the problem of the compensation of sensitivity and resolution/resist pattern under the irradiation with electron beams.
Concerning the crosslinking agents, use has been made of methylolmelamine, resol resins, epoxidized novolak resins, urea resins and the like. However, these crosslinking agents are unstable to heat and thus suffer from a problem of poor storage stability in the form of resist solutions. In addition, these crosslinking agents cannot satisfy the requirements for high sensitivity, high resolution and rectangular resist pattern under the irradiation with electron beams.
Namely, it has been required to establish resist compositions of the negative chemical amplification type for electron beams or X-rays whereby various properties including sensitivity, resolution, resist pattern, development defect, coating properties and solvent-solubility can be satisfied.